Apple released MacBook Air EFI Firmware Update 2.9.1 on Wednesday to replace the problem-ridden 2.9 version it rolled out, and then pulled, earlier in July. The update addresses an issue where the 2011 MacBook Air failed to properly wake from sleep.
Apple released MacBook Air EFI Firmware Update 2.9.1 to replace the buggy 2.9 version
The update, according to Apple's release notes,
...replaces EFI Firmware Update 2.9 and is recommended for MacBook Air (Mid 2011) models. This update addresses an issue where systems may take longer to wake from sleep than expected and fixes a rare issue that may cause fans to run at full speed after waking from sleep.
The original update left some MacBook Air owners with laptops plagued by crashes, so Apple pulled it until those issues could be resolved -- which turned out to be today. MacBook Air EFI Firmware Update 2.9.1 is 4.3 MB and is available for the 2011 MacBook Air via the Software Update application, or as a downloadable installer at the Apple Support website.